Radio frequency circuit and communication system with power amplifier control

ABSTRACT

A radio frequency circuit includes a radio frequency signal source which produces a radio frequency signal, a power amplifier which power amplifies the radio frequency signal from the radio frequency signal source, and a control unit which controls an output power of the power amplifier. Particularly, the control unit is configured to hold control data defining a relationship among an output power, a gain, and an operation bias point of the power amplifier and adjust the operation bias point of the power amplifier based on the control data such that the output power of the power amplifier is set into a level designated by an external power designating instruction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2001-127133 filed Apr. 25,2001, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radio frequency circuit whichcontrols the output power of a radio frequency signal in poweramplification and a communication system equipped with that radiofrequency circuit.

2. Description of the Related Art

In view of reduction in power consumption, transmission power iscontrolled in many radio communication systems including a mobilecommunication system. However, when the output power is lowered,degradation of the power addition efficiency η add occurs in the mainpower amplifier and a driver amplifier located at a preceding stage ofthe main power amplifier. The power addition efficiency η add can beobtained as a result of dividing a difference between the RF input powerP_(rfin) and the RF output power P_(rfout) by the DC input powerP_(dcin). That is, η add=(P_(rfout)−P_(rfin))/P_(dcin).

FIG. 15A shows a conventional radio frequency circuit which cancompensate for degradation of the power addition efficiency. That is,the bias voltage is adjusted to lower the output power, appropriately.For example, when the output power is lowered to ¼, the bias voltage ischanged from B2 to B1 as shown in FIG. 15B. However, the radio frequencycircuit requires a variable voltage source V1 capable of providing alarge current. In general, a DC-DC converter shown in FIG. 15C is usedas the variable voltage source V1, thus increasing the number ofcomponents, the mounting area thereof, and the cost. Further, in thisratio frequency circuit, it difficult to maintain the efficiency becausethe proportion of the knee voltage to the bias voltage increases as theoutput power drops. Moreover, it is difficult to maintain a highefficiency over a wide range of output power because the minimum outputvoltage of the variable voltage source V1 is of the order of 1 V inassociation with the reference voltage of the internal regulator and theefficiency of the DC-DC converter drops at low output voltages. In theradio frequency circuit, a variable voltage source V2 is also used forcontrolling the bias current, which becomes an idle current at zerosignal input. However, the bias current is adjusted such that the powergain of the power amplifier remains unchanged as much as possible evenat low output levels because the radio frequency circuit is provided forthe purpose of keeping the power addition efficiency from decreasingwith decreasing output power.

A method, in which a fixed voltage source is used instead of thevariable voltage source V1 shown in FIG. 15A, has been also proposed.With the method, only the bias current is controlled by the variablevoltage source V2 under the fixed bias voltage. However, the biascurrent is adjusted such that the power gain of the power amplifierremains unchanged as much as possible even at low output levels becausethe radio frequency circuit of this method is also provided for thepurpose of keeping the power addition efficiency from decreasing withdecreasing output power. For example, when the power amplifier includestwo stages of amplification to attain the power gain of about 24 dB atmaximum output, the bias point is adjusted such that the power gain ismaintained at about 21 dB at low output levels as well.

The principle of the conventional method that controls only the biascurrent based on the variable voltage source V2 will be described. FIG.8 shows the relationship between the output power of the power amplifierand the ratio of an undesired signal component to a desired signalcomponent (hereinafter referred to as the U/D ratio) in an RF signaloutput from the power amplifier. The undesired signal is produced due tonon-linearity of the power amplifier. Generally, the voltage source V2is fixed to a voltage value causing that the U/D ratio shifts with aconstant margin with respect to the reference value R upon an increaseof the output power of the power amplifier and exceeds the referencevalue R at maximum output power P as shown in FIG. 8. When the amplifierbias point of V2 is set to a value nearer the class B area than thefixed value, the characteristic curve of the U/D ratio to the outputpower as a whole will move upward in FIG. 8 with a slight change inshape. If a desired output power is lower than the maximum output powerP, the power addition efficiency can be compensated for by adjusting thebias point of V2 to a value near the class B area in a range that theU/D ratio to the output power as a whole does not exceed the referencevalue R.

A radio frequency circuit shown in FIG. 14 is uses as another means forcompensating for deterioration of the power addition efficiency. Withthis radio frequency circuit, power amplifiers different in maximumoutput power, AMP1 (maximum output power: −20 dBmW), AMP2 (5 dBmW) andAMP3 (3 dBmW), are arranged in series via switch circuits S71, S72, S73and S74, and bypass circuits 75 and 76 are arranged in parallel with thepower amplifiers AMP2 and AMP3, respectively. The switch circuits S71,S72, S73 and S74 perform switching between the power amplifier AMP2 andbypass circuit 75 and between the amplifier AMP3 and bypass circuit 76so as to change the configuration of signal paths behind the poweramplifier AMP1.

This radio frequency circuit operates to disconnect unnecessary poweramplifiers at low output power levels and reduce the idle currentdissipated by the power amplifiers. Assume that the switches S71 to S74and the bypass circuits 75 and 76 are free from loss. To provide outputpower higher than 5 dBmW, the amplifiers AMP1, AMP2, and AMP3 will berequired. However, the amplifier AMP3 may be unnecessary anddisconnected when the output power is not higher than 5 dBmW. Likewise,both the amplifiers AMP2 and AMP3 can be unnecessary and disconnectedwhen the output power is not higher than −20 dBmW. Thus, the idlecurrent dissipated by at least one of the amplifiers AMP2 and AMP3 canbe reduced when the output power is below 5 dBmW.

However, although the switch-based method as shown in FIG. 14 isstraightforward, the insertion loss of each of the switches becomes aproblem. In particular, the insertion loss of the switch S74 at theoutput of the final-stage amplifier AMP3 greatly reduces the poweraddition efficiency. Assuming the insertion loss of each switch to be 1dB, the output power of the amplifier AMP3 must be 31 dBmW. If the poweraddition efficiency of the amplifier AMP3 is 40% at maximum output andthe supply voltage and the power gain of the amplifier AMP3 are 3.5 Vand 25 dB, the consumption current will be 896 mA. In the absence of theswitch, the radio frequency circuit has only to produce an output powerof 30 dBmW. The consumption current will be 712 mA in the case where thepower addition efficiency is 40%, the supply voltage is 3.5 V and thepower gain is 25 dB. The insertion of a switch having an insertion lossof 1 dB at the output of the amplifier AMP3 results in an increase ofconsumption current by 1.26 times. This is nothing else but to increasethe device size by 1.26 times in order to increase the output power by 1dB. The consumption current is increased by 1.26 times over the wholerange of output power. Naturally, the idle current is also increasedby 1. 26 times. To compensate for 1 dB of insertion loss of each of theswitches S72 and S73 between the amplifiers AMP2 and AMP3, the amplifierAMP2 is required to compensate for a total of 3 dB including theinsertion loss of the switch S74. In many cases, more stringentdistortion criteria are imposed on the amplifier AMP2 than on theamplifier AMP3 and, to ensure linearity, the power addition efficiencygenerally becomes low, of the order of 4%. Assuming that the outputpower, the power addition efficiency, the supply voltage and the powergain of the amplifier AMP2 are 8 dBmW, 4%, 3 V and 25 dB, respectively,the consumption current will become 52.4 mA. Assuming that the switchesS73 and S74 are removed and the amplifier AMP3 is connected at alltimes, the amplifier AMP2 has only to provide an output power of 6 dBmW,requiring the consumption current to be as low as 33.1 mA. This currentcorresponds to 63% of that when the amplifier AMP3 is bypassed. Further,the consumption current is reduced to 78% in total when the amplifiersAMP2 and AMP3 are bypassed.

Although the switch-based bypassing method apparently seems to be simpleand effective, the consumption current increases greatly with increasingoutput power. Thus, as a conventional manner, the bypass circuit 75 ofthe amplifier AMP2 is used positively while the bypass circuit 76 of theamplifier AMP3 is little used. The provision of switches also causes aproblem of an increase in the number of components, the mounting areathereof, and the signal distortion.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a radio frequencycircuit which can provide a wide dynamic range while reducingsubstantial DC consumption power without increasing the total mountingarea and the number of components.

According to an aspect of the present invention, there is provided aradio frequency circuit comprising: a radio frequency signal sourcewhich produces a radio frequency signal; a power amplifier which poweramplifies the radio frequency signal from the radio frequency signalsource; and a control unit which controls an output power of the poweramplifier, wherein the control unit is configured to hold control datadefining a relationship among an output power, a gain, and an operationbias point of the power amplifier and adjust the operation bias point ofthe power amplifier based on the control data such that the output powerof the power amplifier is set into a level designated by an externalpower designating instruction.

Further, according to another aspect of the present invention, there isprovided a communication system comprising: a radio frequency circuitwhich includes a radio frequency signal source which produces a radiofrequency signal, a power amplifier which power amplifies the radiofrequency signal from the radio frequency signal source, and a controlunit which controls an output power of the power amplifier; and anantenna which radiates the radio frequency signal output from the poweramplifier of the radio frequency circuit; wherein the control unit isconfigured to hold control data defining a relationship among an outputpower, a gain, and an operation bias point of the power amplifier andadjust the operation bias point of the power amplifier based on thecontrol data such that the output power of the power amplifier is setinto a level designated by an external power designating instruction.

With the radio frequency circuit and the communication system, thecontrol unit holds control data defining a relationship among an outputpower, a gain, and an operation bias point of the power amplifier andadjusts the operation bias point of the power amplifier based on thecontrol data such that the output power of the power amplifier is setinto a level designated by an external power designating instruction. Insuch a structure, the gain of the power amplifier can be reduced whenthe output power of the power amplifier is lowered. Thus, a wide dynamicrange can be obtained without increasing the total mounting area and thenumber of components and reduce substantial DC consumption current suchas an idle current which flows in the power amplifier when no signal isinput thereto. In addition, the substantial DC consumption current canbe significantly reduced if the power amplifier becomes to a state wherethe radio frequency signal passes though with no power gain.

Although transmission power is generally monitored in communicationsystem to produce a transmission power control signal, the presentinvention can be achieved regardless of monitoring of the transmissionpower.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a block diagram showing the configuration of a radio frequencycircuit according to one embodiment of the present invention;

FIG. 2 a block diagram showing a modification of the radio frequencycircuit of FIG. 1;

FIG. 3 is a graph showing the control voltage—output powercharacteristic of the radio frequency circuit shown in FIG. 1;

FIG. 4 is a graph showing the adjacent channel leakage power—outputpower characteristic of the radio frequency circuit shown in FIG. 1;

FIG. 5 is a graph showing the power gain—output power characteristic andthe input power—output power characteristic of the radio frequencycircuit shown in FIG. 1;

FIG. 6 is a graph showing a relationship between the consumption currentand the output power of the radio frequency circuit shown in FIG. 1;

FIGS. 7A and 7B are block diagrams showing examples where the radiofrequency circuit shown in FIG. 1 is applied to a terminal device and abase station device for a mobile communication system, respectively;

FIG. 8 is a graph showing a relationship between the U/D ratio and theoutput power of a general class AB linear amplifier;

FIG. 9 is a graph showing a relationship between the DC consumptioncurrent and the RF output power of a general class AB linear amplifier;

FIG. 10 is a graph showing an example of a probability density functionof transmission power in a radio communication system whose transmissionpower is controlled;

FIG. 11 is a graph showing a probability density function of consumptioncurrent derived from the probability density function shown in FIG. 10;

FIGS. 12A and 12B are graphs showing examples of the power additionefficiency and the reciprocal thereof to the output power of a class Bpower amplifier;

FIGS. 13A and 13B are diagrams for use in explanation of a lowering ofthe power addition efficiency in the power amplifier at low output powerlevels;

FIG. 14 is a diagram showing a conventional radio frequency circuit; and

FIGS. 15A, 15B and 15C are diagrams for use in explanation of otherconventional radio frequency circuits.

DETAILED DESCRIPTION OF THE INVENTION

A radio frequency circuit according to one embodiment of the presentinvention will be described with reference to the accompanying drawings.The radio frequency circuit is used for power amplifying a radiofrequency signal for transmission and widely controlling the outputpower of the radio frequency signal in a radio communication system.

Initially, a typical power control and degradation in power additionefficiency caused when the output power is lowered by the control willbe described, so that the operation principle of the radio frequencycircuit can be easily understand. Here, the power addition efficiency isdefined as the RF (Radio Frequency) output power divided by the DC(Direct Current) input power.

FIG. 9 shows a relationship between the DC consumption current and theRF output power of a general power amplifier biased to operate as aclass AB linear amplifier for radio communication. FIG. 10 shows anexample of a probability density function of transmission power in aradio communication system whose transmission power is controlled. Inthis example, the transmission power reaches a maximum of 30 dBmW andthe power that is highest in the probability of being transmitted liesin the vicinity of 10 dBmW. The transmission power may take values ofless than 0 dBmW.

Referring to FIG. 9, the consumption current seems to increase withincreasing RF output power. If the power addition efficiency is constantregardless of the output power, the consumption current of 400 mA at 30dBmW should be 40 mA at 20 dBmW, which is one-tenth of 400 mA. However,in this example, 130 mA is consumed because the power additionefficiency is degraded as the output power decreases.

With RF output power levels of less than 10 dBmW, the consumptioncurrent approaches a finite constant value regardless of the RF outputpower. In the example of FIG. 9, the consumption current is about 60 mAand called as the idle, set, or quiescent current for biasing the poweramplifier to operate as a class AB amplifier.

If the power amplifier is biased to operate as a class B amplifier, theconsumption current at low output power levels approaches 0. In the caseof a power amplifier for linear modulation, it is necessary to suppressdistortion by biasing the power amplifier to operate as a class ABamplifier. In the case of the class AB amplifier, useless current thatdoes not contribute to RF power is consumed at low output levels.Applying the probability density function of transmission power shown inFIG. 10 to the relationship between the DC consumption current and theRF output power shown in FIG. 9 results in the probability distributionfunction of the consumption current, which is indicated by a solid curvein FIG. 11. The dashed line indicates the average consumption current ofthe order of 84 mA. A current of about 60 mA, which is the idle current,is consumed with a probability of more than 50%. The probability ofconsumption currents of more than 100 mA is 14%. The probability ofconsumption currents of more than 200 mA is 3.5%. The probability ofconsumption currents of more than 300 mA is no more than 1%. From FIG.11 it is seen that the average consumption current depends on the idlecurrent. With radio communication systems whose the transmission poweris controlled over a wide range, it is very important to reduce the idlecurrent in the power amplifier.

FIG. 12A shows an example of the power addition efficiency to the outputpower of a class B power amplifier, in which the idle current is zero.As shown in FIG. 12A, the power addition efficiency of the poweramplifier becomes maximum in the vicinity of saturated output power anddeclines at low power levels. As described above, the power additionefficiency is defined as the RF output power divided by the DC inputpower. Thus, the power addition efficiency corresponds to the collectorefficiency in the case of bipolar transistors and the drain efficiencyin the case of field effect transistors. FIG. 12B shows the reciprocalof the power addition efficiency of FIG. 12A in logarithmic scale. Theratio of the DC input power to the RF output power of the poweramplifier could be seen from FIG. 12B. The power addition efficiency isreduced from 72% at 30 dBmW through 21.8% at 20 dBmW and 4.7% at 10 dBmWdown to 1.5% at 5 dBmW. The ratio of the DC input power to the RF outputpower increases from 1.4 at 30 dBmW through 4.6 at 20 dBmW and 21.2 at10 dBmW up to 67.1 at 5 dBmW. Thus, useless DC input power that does notcontribute to RF output power is consumed at low output power levels.

The principle on which, at low output levels, the power additionefficiency decreases will be described with reference to FIGS. 13A and13B. It is assumed that the power amplifier is of a simply idealizedtransistor model. A dynamic load line is obtained by superimposinginstantaneous current and voltage values on static characteristics, andrepresented by a crooked line KBC. The output voltage is represented bya sinusoidal wave whose average value corresponds to the bias voltage.The output current is represented by half-wave rectified waves. Thepower amplifier performs the class B operation with the bias pointindicated by the point B in FIG. 13A. The RF output power is given bythe product of the effective value of the fundamental-wave componentVout(t) of the output voltage and the effective value of thefundamental-wave component I1(t) of the output current. Thus, the RFoutput power corresponds to half the area of the quadrangle surroundedby a dotted line in FIG. 13A with the points R and B used as oppositecorners. The DC input power is given by the product of the bias voltageand the average of the output current Iout(t). Thus, the DC input powercorresponds to the area of the quadrangle defined by a broken line inFIG. 13A with the points D and B used as opposite corners. If the gainof the power amplifier is sufficiently high, the power additionefficiency corresponds to the ratio in area between both quadrangles.The straight line connecting the points R and B forms the load line forthe fundamental wave.

When both the current amplitude and the voltage amplitude are halvedfrom the values shown in FIG. 13A to the values shown in FIG. 13B, theRF output power is reduced to one fourth. On the other hand, the DCcurrent is reduced in the same proportion, i.e., halved because it isthe average of the RF current, while the DC voltage is fixed at point B.Therefore, the area of the quadrangle defined with the points D and Bused as opposite corners is halved. As a result, the power additionefficiency is halved each time the RF output power is reduced to onefourth (−6 dB). Thus, the power addition efficiency in the poweramplifier is degraded at low output power levels.

The principles of the present invention will be described below. FIG. 8is a graph showing a characteristic curve which represents therelationship between the output power of a general linear RF poweramplifier biased to operate as a class AB amplifier and the ratio of anundesired signal component to a desired signal component (hereinafterreferred to as the U/D ratio) in an RF signal output from the poweramplifier. Here, the undesired signal refers to signal distortions thatcause adjacent channel leakage power and third harmonic distortion.Further, EVM (Error Vector Mean) may be caused by signal distortions.However, EVM is not in FIG. 8. These signal distortions are prescribedas important matters in radio communication. In FIG. 8, the U/D ratio isshown oh the vertical axis and the output power is shown on thehorizontal axis. As to the undesired signal, a distortion referencevalue R is set up for each radio communication system used. Theallowable distortion is shared among components in the radiocommunication system to determine the final distortion reference value Rfor the power amplifier. The power amplifier used is required to meetthis distortion reference value. That is, in the power amplifier, theU/D ratio to whole output power maintained to be less than thedistortion reference value R. In FIG. 8, P represents the maximum outputpower that meets the distortion reference value R.

With general RF linear amplifiers as shown here, there is a tendencythat the U/D ratio increases with increasing output power. The matchingcircuit and the bias point of the power amplifier are thereforeoptimized at the output power P. Unless the bias point is controlledaccording to the output power, therefore, the characteristic curve willhave an inflection point as indicated by a solid line in the graph. Thecurve is characterized in that as the output power increases, anincrease in the U/D ratio temporarily becomes gentle and, depending oncircumstances, the ratio temporarily decreases and then increasessharply as shown in FIG. 8. In general, the curve has a tendency tobecome linear as the operation approaches the class A operation andascend or descend abruptly as the operation approaches the class Boperation.

In power amplifiers, as the operation approaches the class A operation,the distortion decreases but the power addition efficiency declines and,as the operation approaches the class B operation, the distortionincreases but the power addition efficiency improves. A tradeoff isinvolved between distortion and power addition efficiency.

In the class A operation, the load line is formed by the line connectingthe points K and C in FIG. 13A. The current Iout(t) becomes sinusoidaland the idle current corresponds to half the amplitude. In the class Boperation, the idle current becomes zero at the bias point B. That is,from the point of view of power addition efficiency improvement and idlecurrent reduction, the choice of operation that is close to the. class Boperation is favorable.

As is evident from FIG. 8, the displacement of the U/D ratio from thereference value R increases with decreasing output power. At low outputpower levels, it is therefore important to operate the power amplifierat a deeper bias point (as close to the class B operation as possible).

FIG. 1 shows the configuration of the radio frequency circuit accordingto the embodiment of the present invention. The radio frequency circuitproduces a radio frequency signal, a power amplifier 12 that amplifiesthe power of the radio frequency signal output from the radio frequencysignal source 11, and a control unit 18 that controls the output powerof the radio frequency signal source 11 and the output power of thepower amplifier 12. In FIG. 1, 13 denotes the radio frequency signaloutput from the radio frequency signal source 11 and input to the poweramplifier 12, 14 denotes the radio frequency signal output from thepower amplifier 12, 15 denotes the control terminal of the poweramplifier 12, 16 denotes a first control signal supplied from thecontrol unit 18 to the radio frequency signal source 11 to adjust theoutput power of the radio frequency signal source 11, and 17 denotes asecond control signal supplied from the control unit 18 to the controlterminal 15 of the power amplifier 12 to adjust the operation bias pointof the power amplifier 12. The radio frequency circuit further comprisesa data table 19 that stores control data defining a relationship amongan operation bias point Vb of the power amplifier 20 and at least two ofthree items such as the input power Pin, power gain Ga and output powerPout that determine the operation bias point Vb. The control unit 18receives an output power designating instruction 20 from a controller,such as a CPU, that controls the entire communication system.

The following is an example of the data table 19.

TABLE 19 Pout (dBmW) Vb (V) Pin (dBmW) 28.18 2.9 4 26.89 2.62 3.8 24.92.66 1.8 22.39 2.67 −0.2 19.94 2.67 −2.2 17.38 2.67 −4.2 14.61 2.65 −6.211.61 2.65 −8.2 8.23 2.62 −10.2 5.77 2.59 −11.2 2.87 2.55 −12.2 −7.642.35 −13.2 −13.48 2.01 −14.2 −15.88 2.01 −16.2

The control terminal 15 is adapted to set and vary the operation biaspoint of the power amplifier 12 based on the second control signal 17supplied to adjust the output power. One example of the control terminalis a terminal which, when the power amplifier 12 is comprised of acommon-emitter bipolar transistor, is connected directly or through abias circuit to the base of the transistor.

In the case of digital control, the second control signal 17 is producedfrom the control unit 18 as at least two discrete values. The directionof signal currents between the control unit 18 and the control terminal15 and the driving method (current driving or voltage driving) depend onthe internal circuit configuration of the power amplifier 12.

To facilitate the understanding of the present invention, the voltagedriving is described herein, which is such that a shallow bias pointnear the class A area is set on the high level side and a deep biaspoint near the class B area is set on the low level side. Of course, inactual circuits, this relation may be reversed.

In a case where the power amplifier 12 is comprised of a plurality ofstages, the provision of one control terminal for each stage isdesirable for fine control. To prevent the explanation from becomingcomplex, an example of using a single control terminal will bedescribed.

First, the control operation will be described with reference to FIG. 8.Conventionally, the bias point and the matching point are optimized atthe maximum output power P so that the U/D ratio exceeds the referencevalue R for the output power more than the maximum output power P. Forconvenience sake we shall refer the output power dependence of the U/Dratio and the bias voltage at this time as the conventional U/D ratioand the conventional bias point, respectively. In FIG. 8, there isillustrated the conventional U/D ratio when the second control signal 17is fixed at the conventional bias point.

The control unit 18 performs control in such a way that the U/D ratiobecomes more than the conventional U/D ratio but less than thedistortion reference value R at output power levels lower than themaximum output power P.

That is, the second control signal 17 chooses a bias point which isnearer the class B area than the conventional bias point; therefore, theoutput power that can meet the reference value R falls below the maximumoutput power P. In general, the nearer the class B area the bias pointis, the lower the power gain becomes. In the embodiment, therefore, inorder to allow the distortion reference value R to be met even when theoperation bias point is changed, two of the output power Pout, the powergain Ga and the input power Pin are stored in the data table 19 for eachoperation bias point. By having two items of control data selected fromthe output power Pout, the power gain Ga and the input power Pin, theremaining control data can be determined from the relation such thatPin(dBmW)+Ga(dB)=Pout(dBmW).

In response to the output power designating instruction 20 from theradio communication system, the control unit 18 produces the secondcontrol signal 17 to set an optimum operation bias point at which theU/D ratio is below but in the neighborhood of the distortion referencevalue R. The power gain Ga of the power amplifier 12 is then determined.Thus, the input power Pin of the power amplifier 12, i.e., the power ofthe radio frequency signal 13, is adjusted based on the first controlsignal so as to satisfy Pin(dBmW)+Ga(dB)=Pout(dBmW).

In the embodiment, the voltage of the second control signal 17 islowered for an output power lower than the maximum output power P,thereby setting the operation bias point of the power amplifier 12 inthe class B area deeper than the conventional bias point.

The contents of the data table 19 are determined in the followingmanner. When the power amplifier 12 is determined to be used in theradio communication system, one of its input power Pin, output powerPout and power gain Ga is decided and then conditions under whichanother satisfies the distortion reference value R are measured. Forexample, the input power Pin is decided by means of the first controlsignal, and the bias point is adjusted through the second control signal17 to search for a value for which the U/D ratio satisfies thedistortion reference value R. The output power Pout is measured for theinput power Pin and the bias point. The gain Ga is obtained by theaforementioned relationship, that is, Pin(dBmW)+Ga(dB)=Pout(dBmW).

The radio frequency signal source 11 includes at least an outputadjusting unit, such as a gain controlled amplifier or attenuator. Inaddition, it may further contain a baseband unit, a D/A converter, amodulator, an upconverter, etc. The radio frequency signal 13 has itspower controlled by the output adjusting unit and then input to thepower amplifier 12.

In order to control the power of the radio frequency signal 14 outputfrom the power amplifier 12, the control unit 18 produces the first andsecond control signals that control the radio frequency signal source 11and the power amplifier 12, respectively. When there is no need ofoutputting the radio frequency signal 14, the radio frequency signalsource 11 and the power amplifier 12 are switched OFF (shut down) so asto eliminate power dissipation.

Upon reception of the output power designating instruction 20 from thecontroller, such as a CPU, that controls the operation of the entirecommunication system, the control unit 18 reads from the data table 19the input power Pin of the power amplifier 12 and the bias point for thepower gain Ga of the power amplifier 12 corresponding to the outputpower designating instruction 20. Thus, if the contents of the datatable 19 are formed of a combination of the input power Pin and thepower gain Ga or the output power Pout and the power gain Ga, but not acombination of the input power Pin and the output power Pout, theremaining data is determined from the relation among Pin, Pout and Ga.

Since the contents of the data table 19 are discrete data, the controlunit 18 interpolates these data by an interpolation method such aslinear interpolation or spline interpolation, as required. Theinterpolation may be performed through either anti-logarithm orlogarithm.

In the radio frequency circuit of the embodiment, upon reception of theoutput power designating instruction 20, the control unit 18 refers tothe data table in order to control the output power Pout of the poweramplifier 12 in accordance with the output power designating instruction20. That is, the control unit obtains the input power Pin of the poweramplifier 12 for the output power Pout designated by the output powerdesignating instruction 20 and then produces the first control signal 16for the input power Pin. The output power of the radio frequency signalsource 11 is specified by the first control signal 16. Further, thecontrol unit 18 obtains the power gain Ga for the output power Poutdesignated by the output power designating instruction 20 and thenproduces the second control signal 17 for the power gain Ga. Theoperation bias point of the power amplifier 12 is specified by thesecond control signal 17. Here, as described previously, the secondcontrol signal 17 has its voltage lowered at output power levels lowerthan at maximum output power P. As a result, at all output power levelsthe operation bias point can be set in the class B area deeper than theconventional bias point within the range in which the distortionreference value R is satisfied.

Further, the control unit 18 sets, through the second control signal 17,the operation bias point not only in the class B area deeper than theconventional bias point but also in the area near pinch-off (cutoffregion) in order to perform gain control for lowering the power gain Gaof the power amplifier 12. Thereby, the power amplifier 12 is placed inthe through state to allow the radio frequency signal to pass throughwithout any power gain, which results in a significant reduction inconsumption current of the power amplifier 12 such as the idle currentin class AB amplification. Thus, the consumption current of the entireradio communication system that requires transmission power control canbe reduced significantly.

FIG. 2 shows a modification of the radio frequency circuit shown inFIG. 1. This modification is similar to the radio frequency circuitshown in FIG. 1 except for a temperature compensation configuration forthe power amplifier 12. Thus, similar parts to those in FIG. 1 aredenoted by the same reference numerals and descriptions thereof areomitted.

In this modification, the control unit 18 supplies the second controlsignal 17 to a control signal converter 21 in place of the controlterminal 15 of the power amplifier 12. The control signal converter 21converts the second control signal 17 into a third control signal toserve as a bias circuit for temperature compensation of the poweramplifier 12, and supplies the third control signal to the controlterminal 15 of the power amplifier 12. Although, in FIG. 2, the controlsignal converter 21 is provided independently of the power amplifier 12,they may be incorporated into one package, module, or integratedcircuit.

The results of experiments on the radio frequency circuit shown in FIG.1 with the distortion reference value taken as −38 dBc are shown inFIGS. 3 to 6. FIG. 3 shows the control voltage—output powercharacteristic of the power amplifier 12 and FIG. 4 shows the adjacentchannel leakage power—output power characteristic of the power amplifier12. The control voltage is conventionally fixed to a level indicated bya dotted line. Thus, the adjacent channel leakage power decreases withdecreasing output power and takes values much lower than the referencevalue (=−38 dBc). In contrast, in the embodiment, the second controlsignal 17 is input as a control voltage to the control terminal 15 ofthe power amplifier 12. The control voltage changes, as indicated by asolid line, from 2.9 to 2 V with decreasing output power with theadjacent channel leakage power kept at −38 dBc. Thereby, the power gainof the power amplifier 12 is varied accordingly.

FIG. 5 shows the power gain—output power characteristic and the inputpower—output power characteristic of the power amplifier 12. The controlvoltage is conventionally fixed. Thus, the power gain Ga indicated by adotted line depends little on the output power. In contrast, in theembodiment, the power gain Ga is lowered to the neighborhood of 0 dB atlow output power levels and hence can be controlled over a range of 25dB.

In the embodiment, the input power Pin is limited in accordance with thecontrol voltage so as to satisfy the reference value, −38 dBc, of theadjacent channel leakage power.

FIG. 6 shows a relationship between the consumption current and theoutput power of the radio frequency circuit 12. The control voltage isconventionally fixed. Thus, the consumption current approaches an idlecurrent of 70 mA at low output power levels, as indicated by a dottedline. In the embodiment, the consumption current is reduced to 7 mAwhich is about 1/10 of the idle current. As a result of evaluating thisresult using the probability density function of transmission power, theconsumption current can be reduced by up to 50%.

As can be seen from FIGS. 5 and 6, according to the embodiment, byreducing the power gain Ga by 9 dB from 24 to 15 dB to make the outputpower less than ⅛ of the maximum output power, the consumption currentcan be reduced remarkably. Further, by lowering the power gain Ga downto 6 dB, the consumption current can be further reduced. Even if thepower gain Ga lies in the range of 0 to −3 dB, the consumption currentcan be reduced. That is, when the power gain Ga is set at about 0 dB inthe range of 6 to −3 dB, the consumption current can be furtherdecreased. In this embodiment, the data table 19 is referred to even iftemperature or frequency fluctuates. It is desirable to refer to othertables which are prepared to cope with fluctuation of temperature andfrequency, as required.

As described above, the radio frequency circuit according to theembodiment is especially suitable for systems that require a poweramplifier having a wide range of output power. For example, the circuitis useful for communication with mobiles or, even with communicationbetween fixed stations, when the radio wave propagation environment isliable to variations. In particular, the circuit is well-suited formobile communication systems for portable phones, radio access systemsexemplified by radio LAN equipment, and, most of all, CDMA (CodeDivision Multiple Access)-based systems that require a wide dynamicrange.

Next, an example in which a radio communication system shown in FIG. 1is applied to a terminal device of the mobile communication system willbe described. FIG. 7A shows the configuration of the terminal device ofthe mobile communication system. The terminal device comprises, as shownin FIG. 7A, a transceiver 100 and antennas 101 and 102 coupled to thetransceiver 100. The transceiver 100 includes an antenna switch 103 forswitching between the antennas 101 and 102, an amplifier 104 foramplifying radio frequency signals to be radiated by the antennas 101and 102, an amplifier 105 for amplifying radio frequency signalsreceived by the antennas 101 and 102, a modulator 106 for modulating aradio frequency signal to be supplied to the amplifier 104, ademodulator 108 for demodulating a radio frequency signal from theamplifier 105, and a radio frequency synthesizer 107 for producingfrequencies for transmission and reception. The amplifier 104 is formedof the radio frequency circuit described in conjunction with FIG. 1. Theterminal device further comprises an input and output unit 110 thatserves as an interface with input and output signals, a baseband signalprocessor 109 that performs baseband signal transformation processingbetween the input and output unit 110 and the transceiver 100, and acontrol unit 111 that controls the input and output unit 110 and thetransceiver 100. The transceiver 100, the baseband signal processor 109and the input, and output unit 110 are operated from the supply voltageof a power supply 112. The input and output unit 110 includes amicrophone 110 a that enters audio signals such as voice, a keypad 110 dthat enters characters such as letters, numerals and the like, aloudspeaker 110 b that outputs audio signals such as voice in the formof sound energy, a display 110 c that displays letters, numerals, andgraphic images, a vibrator 110 e that produces vibrations, and a datainput and output module 110 f that electrically, magnetically, oroptically inputs and outputs various pieces of data. The data input andoutput module 110 f corresponds to a Bluetooth module, an interface forperipheral equipment such as USB or IEEEI 394, an interface for a memorycard such as a CF (Compact Flush) card or a SD (Super Density) card, oran interface for connection to a host such as a personal digitalassistant (PDA) or a personal computer.

In this terminal device, various signals are input from the microphone110 a, the keypad 110 d, and the data input and output unit 110 f in theinput and output unit 110. These signals are processed in the basebandsignal processor 109, and then modulated in the modulator 106 andapplied to the amplifier 104 as radio frequency signals under thecontrol of the control unit 111. The amplifier 104 processes the radiofrequency signal from the modulator 106 in the same manner as the radiofrequency circuit shown in FIG. 1 and outputs it as a transmission radiofrequency signal to be transmitted from the antennas 101 and 102 throughthe antenna switch 103.

A radio frequency signal received by each of the antennas 101 and 102 isamplified in the amplifier 105 and then demodulated in the demodulator108 into a baseband signal, which is in turn converted by the basebandsignal processor 108 into a control signal that controls the loudspeaker110 b, the display 110 c, the vibrator 110 e, or the data input andoutput module 110 f. These operations are made under the control of thecontrol unit 111.

Here, an example in which the radio frequency circuit shown in FIG. 1 isapplied to a base station device of the mobile communication system willbe described. FIG. 7B shows the configuration of the base station deviceof the mobile communication system. As shown in FIG. 7B, the basestation device comprises a plurality of transceivers 200 and pairs ofantennas 201 and 202, each pair being coupled to a corresponding one ofthe transceivers 200. Each of the transceivers 200 includes an antennaswitch 203 for switching between the antennas 201 and 202 of acorresponding pair, an amplifier 204 for amplifying radio frequencysignals to be radiated by the antennas 201 and 202, an amplifier 205 foramplifying radio frequency signals received by the antennas 201 and 202,and a modulation and demodulation module 206 for modulating a radiofrequency signal to be supplied to the amplifier 204 and demodulating aradio frequency signal from the amplifier 205. The amplifier 204 isformed of the radio frequency circuit described in conjunction withFIG. 1. The base station device further comprises a baseband signalprocessor 207, a network interface 208, and a control unit 209. Thenetwork interface 208 makes connection between channels. The basebandsignal processor 207 performs baseband signal transformation processingbetween the network interface 208 and the transceivers 200. The controlunit 209 controls the baseband signal processor 207, the networkinterface 208, and the transceivers 200. The transceivers 200, thebaseband signal processor 207 and the network interface 208 are operatedfrom the supply voltage from a power supply 210.

In this base station device, an external signal input through thenetwork interface 208 is processed in the baseband signal processor 207,then modulated in the modulation and demodulation module 206 and appliedto the amplifier 204 as a radio frequency signal. The amplifier 204processes the radio frequency signal from the modulation anddemodulation module 206 in the same manner as the radio frequencycircuit shown in FIG. 1 and outputs it as a transmit radio frequencysignal to be transmitted from the antennas 201 and 202 through theantenna switch 203.

A radio frequency signal received by each of the antennas 201 and 202 isamplified in the amplifier 205 and then demodulated in the modem 206into a baseband signal, which is in turn converted by the basebandsignal processor 207 into a control signal and then output to theoutside. These operations are made under the control of the control unit209.

According to the aforementioned radio frequency circuit, the consumptioncurrent in a power amplifier for a control of transmission power can bereduced to 1/10 of that in the conventional circuit at low output powerlevels. This excellent characteristic allows the effective averageconsumption current associated with output power control to be reducedby up to 50%. The circuits necessary for the radio frequency circuit canbe integrated into an MMIC or LSI chip, allowing the inventive radiofrequency circuit to be applied to the power amplifier in portablephones required to be small and inexpensive.

The aforementioned embodiment can be modified. For example, instead ofusing the data table 19 of FIG. 1, control data which define arelationship of at least two of the input power, power gain and outputpower and the corresponding operation bias point may be provided in theform of a function described by a software program. These control datamay be output in analog form through hardware such as operationalamplifiers.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiment shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A communication system comprising: a radio frequency circuit whichincludes a radio frequency signal source which produces a radiofrequency signal, a power amplifier which power amplifies the radiofrequency signal from said radio frequency signal source, and a controlunit which controls an output power of the power amplifier; and anantenna which radiates the radio frequency signal output from the poweramplifier of said radio frequency circuit; said control unit beingconfigured to hold control data defining a relationship among anoperation bias point of said power amplifier and at least two of aninput power, and a gain and the output power of said power amplifier,and to adjust the operation bias point of said power amplifier based onthe control data such that the output power of said power amplifier isset into a level designated by an external power designatinginstruction; wherein when the external power designating instructiondesignates a maximum output power of said power amplifier, saidoperation bias point is adjusted to a value nearer a class B area thanthat for the maximum output power within a range that a ratio of anundesired signal component to a desired signal component of the radiofrequency signal from said power amplifier is maintained below adistortion reference value specified for a radio communication system,and said control data are referred to for controlling the sum of theinput power and the gain of said power amplifier to be equal to theoutput power of said power amplifier.
 2. The communication systemaccording to claim 1, wherein said control unit is further configured tochange an output power of said radio frequency signal source based onthe control data.
 3. The communication system according to claim 1,wherein said control unit includes a data table storing control data. 4.The communication system according to claim 1, wherein said control unitincludes a software program described as a function of producing thecontrol data.
 5. The communication system according to claim 1, whereinsaid control unit includes a hardware that outputs the control data inan analog form.
 6. A communication system comprising: a radio frequencycircuit which includes a radio frequency signal source which produces aradio frequency signal, a power amplifier which power amplifies theradio frequency signal from said radio frequency signal source, and acontrol unit which controls an output power of the power amplifier; andan antenna which radiates the radio frequency signal output from thepower amplifier of said radio frequency circuit; said control unit beingconfigured to hold control data defining a relationship among anoperation bias point of said power amplifier and at least two of aninput power, and a gain and the output power of said power amplifier,and to adjust the operation bias point of said power amplifier based onthe control data such that the output power of said power amplifier isset into a level designated by an external power designatinginstruction; wherein said control data are results obtained by measuringat least two of the input power, power gain and output power whichdefine every operation bias point allowing said power amplifier to serveas a class A to B amplifier within a range that a ratio of an undesiredsignal component to a desired signal component of the radio frequencysignal from said power amplifier is maintained below and in theneighborhood of a distortion reference value specified for a radiocommunication system with respect to an entire output power range ofsaid power amplifier, and said control data are referred to forcontrolling the sum of the input power and the gain of said poweramplifier to be equal to the output power of said power amplifier.
 7. Acommunication system comprising: a radio frequency circuit whichincludes a radio frequency signal source which produces a radiofrequency signal, a power amplifier which power amplifies the radiofrequency signal from said radio frequency signal source, and a controlunit which controls an output power of the power amplifier; and anantenna which radiates the radio frequency signal output from the poweramplifier of said radio frequency circuit; said control unit beingconfigured to hold control data defining a relationship among anoperation bias point of said power amplifier and at least two of aninput power, and a gain and the output power of said power amplifier,and to adjust the operation bias point of said power amplifier based onthe control data such that the output power of said power amplifier isset into a level designated by an external power designatinginstruction; wherein said control unit is configured to obtain first andsecond control signals based on the control data when the output powerdesignating instruction designates a maximum output power of said poweramplifier, said first control signal adjusting the output power of saidpower amplifier to a maximal level in which a ratio of an undesiredsignal component to a desired signal component of the radio frequencysignal from said power amplifier is maintained below a distortionreference value specified for a radio communication system, said secondcontrol signal adjusting the output power of said radio frequency signalsource to a level in which a power gain of said power amplifier becomesless that ⅛ of that for the maximum output power, and said control dataare referred to for controlling the sum of the input power and the gainof said power amplifier to be equal to the output power of said poweramplifier.
 8. The communication system according to claim 7, whereinsaid control unit is configured to perform interpolation of the controldata in production of the first and second control signals.
 9. Thecommunication system according to claim 7, wherein said control unitincludes a control signal converter that converts the first controlsignal into a third control signal by which a temperature of said poweramplifier is additionally compensated for.